The Obama administration is working to forge a sweeping international climate change agreement to compel nations to cut their planet-warming fossil fuel emissions, but without ratification from Congress. In preparation for this agreement, to be signed at a United Nations summit meeting in 2015 in Paris, the negotiators are meeting with diplomats from other countries to broker a deal to commit some of the world’s largest economies to enact laws to reduce their carbon pollution. But under the Constitution, a president may enter into a legally binding treaty only if it is approved by a two-thirds majority of the Senate. To sidestep that requirement, President Obama’s climate negotiators are devising what they call a “politically binding” deal that would “name and shame” countries into cutting their emissions. The deal is likely to face strong objections from Republicans on Capitol Hill and from poor countries around the world, but negotiators say it may be the only realistic path.

American negotiators are instead homing in on a hybrid agreement — a proposal to blend legally binding conditions from an existing 1992 treaty with new voluntary pledges. The mix would create a deal that would update the treaty, and thus, negotiators say, not require a new vote of ratification. Countries would be legally required to enact domestic climate change policies — but would voluntarily pledge to specific levels of emissions cuts and to channel money to poor countries to help them adapt to climate change. Countries might then be legally obligated to report their progress toward meeting those pledges at meetings held to identify those nations that did not meet their cuts. The strategy comes as scientists warn that the earth is already experiencing the first signs of human-caused global warming — more severe drought and stronger wildfires, rising sea levels and more devastating storms. In seeking to go around Congress to push his international climate change agenda, Mr. Obama is echoing his domestic climate strategy. In June, he bypassed Congress and used his executive authority to order a far-reaching regulation forcing American coal-fired power plants to curb their carbon emissions.